It is well known to provide liquid fabric conditioning compositions which soften in the rinse cycle.
Such compositions comprise less than 7.5% by weight of softening active, in which case the composition is defined as “dilute”, from 7.5% to about 30% by weight of active in which case the compositions are defined as “concentrated” or more than about 30% by weight of active, in which case the composition is defined as “super-concentrated”.
Concentrated and super-concentrated compositions are desirable since these require less packaging and are therefore environmentally more compatible than dilute or semi-dilute compositions.
A problem frequently associated with concentrated and superconcentrated compositions, as defined above, is that the product is not stable upon storage, especially when stored at high temperatures. Instability can manifest itself as a thickening of the product upon storage, even to the point that the product is no longer pourable.
The problem of thickening upon storage is particularly apparent in concentrated and superconcentrated fabric softening compositions comprising an ester-linked quaternary ammonium fabric softening material having one or more fully saturated alkyl chains.
However, it is desirable to use ester-linked compounds due to their inherent biodegradability and to use substantially fully saturated quaternary ammonium fabric softening compounds due to their excellent softening capabilities and because they are more stable to oxidative degradation (which can lead to malodour generation) than partially saturated or fully unsaturated quaternary ammonium softening compounds.
Of the types of ester-linked quaternary ammonium materials known, it is desirable to use those based on triethanolamine which produce at least some mono-ester linked component and at least some tri-ester linked component since the raw material has a low melting temperature which enables the manufacturing process of the composition to occur at low temperatures. This reduces difficulties associated with high temperature handling, transport and processing of the raw material and compositions produced therefrom.
A further problem known to affect concentrated and super-concentrated fabric softening compositions is that the initial viscosity of a fully formulated composition can be very high, up to a point that the composition is substantially unpourable.
The problem of undesirably high initial viscosity and visco-stability upon storage has previously been addressed in various ways.
For instance, EP-A2-0415698 (Unilever) discloses the use of electrolytes, polyelectrolytes, or decoupling polymers to reduce the initial viscosity of fabric softening compositions.
It is also known that an input of energy such as milling or shearing of the product can reduce product viscosity. However, compositions produced by both of these approaches can suffer from colloidal instability. Also, milling or shearing products in a manufacturing process on an industrial scale is time consuming and expensive.
DE 2503026 (Hoechst) discloses formulations comprising 3–12% of a softener (a mixture of non-ester quaternary ammonium compounds imidazoline group containing compounds), 1–6% of a cationic disinfectant, 0.1–5% of a lower alcohol, 0.5–5% of a fatty alcohol and 0–5% of a nonionic emulsifier.
WO 99/50378 (Unilever) relates to compositions comprising from 1 to 8% of quaternary ammonium compound, a stabilising agent and a fatty alcohol. The fatty alcohol is present in order to thicken the dilute composition. The disclosure only relates to dilute compositions and so is not in any way directed to the problem addressed by the present invention of high temperature storage stability of concentrated compositions.
U.S. Pat. No. 4,844,823 (Colgate-Palmolive) discloses a composition comprising 3 to 20% by weight of the combination of a mixture of quaternary ammonium fabric softening compound and fatty alcohol in a weight in a weight ratio 6:1 to 2.8:1. Only non-ester quaternary ammonium compounds are exemplified and there is no disclosure or teaching of fully saturated quaternary ammonium compounds.
The prior art does not address nor give any suggestion how to overcome high initial viscosity and/or high temperature storage stability problems in concentrated compositions comprising fully hardened quaternary ammonium ester linked compounds based on triethanolamine.
WO 93/23510 (Procter & Gamble) mentions fatty alcohols and fatty acids as optional nonionic softeners and teaches that they can improve the fluidity of premix melts. There is no reference to reducing the viscosity of dispersions made from premix melts.
WO 98/49132, U.S. Pat. No. 4,213,867, U.S. Pat. No. 4,386,000, GB-A-2007734, DE 2503026, DE 3150179, U.S. Pat. No. 5,939,377, U.S. 93,915,867 and U.S. Pat. No. 3,644,203 all disclose fabric conditioning compositions comprising fatty alcohols. Fatty alcohols are known as co-softeners and for increasing the viscosity of compositions.